1. Field
This application relates generally to devices and methods to identify target sites for implantation of microstimulators.
2. General Background and State of the Art
Microstimulators such as the BION® implants are intended to be injected through an insertion tool similar to a large hypodermic needle (Kaplan & Loeb, patent pending). Percutaneous intramuscular wire electrodes are injected similarly through a smaller needle. The target site is usually the nerve entry zone of a specific muscle, since all of the motor axons innervating the muscle fibers will then pass close enough to the stimulation electrodes so that they can be recruited as the stimulus intensity is increased over a reasonable range.
In one approach, the clinician implanting the stimulator typically applies trial stimulation pulses through the tip of the insertion tool in order to determine whether it is located appropriately before releasing the electrodes into the tissue. When the tool is correctly located, the clinician will be able to see or feel a twitch of the correct muscle at a relatively low stimulation pulse intensity called threshold. However, simultaneously moving the tool and adjusting the stimulation intensity to determine this threshold is now difficult to do and usually requires two people and considerable discussion between them. The clinician handling the insertion tool wears sterile gloves and may need both hands to operate the tool and palpate the muscle while an assistant adjusts the stimulation intensity according to verbal instructions.